1. Field of Invention
The invention relates to modular tactile surfaces which are applied to roads, walkways and other areas of pedestrian traffic for providing guidance to persons who are visually handicapped. More specifically, the present invention relates to rigid tiles having circular and elongated tactile projections which alert the blind to hazardous conditions or provide travel directions.
2. Prior Art
In an earlier patent, U.S. Pat. No. 4,715,743, the present inventor disclosed an improved tactile tile which included an arrangement of projecting bumps configured either as dots or bars. These respective tiles are illustrated in FIGS. 1 and 3 of that patent. The dot tile of FIG. 1 includes a flat plate 10 comprised of a single layer of flexible plastic or rubber having a top surface 11 and a bottom surface 12. The peripheral edge 14 was chamfered from the plate thickness down to approximately 1 millimeter. The primary purpose for this chamfered configuration was to provide improved adhesion of the periphery of the tile to the road or sidewalk surface. Rubber tiles prior to this configuration would tend to lift at the tile edge, creating a safety hazard as the tile periphery would project upward. As dust, sand or water fell into this detached area, further detachment would occur, until the tile edge was sufficiently raised to trip or otherwise interfere with pedestrian movement.
The chamfered edge provided reduced tendency to curl up because of the reduced thickness. A surrounding gasket formed between tiles by the adhesive applied underneath the tile further contributed to retention of the chamfered edge. As the tile and attached mastic were pressed against the sidewalk or other support surface, the mastic would flow and partially escape through the peripheral crack between adjacent tiles. A sufficient quantity of mastic could seep through this crack, forming a bead which extended over the chamfered edge of the tile. This operated to not only lock the tile in place, but also blocked water and dirt from creeping under the tile to thereby weaken the bonded connection.
This flexible tile configuration was adopted because it offered two features considered important to the visually handicapped. The first feature was a resilient aspect provided by the rubber composition. This resilience appeared to enhance the sensitivity of the foot for tactile detection. As was stated in column 6, lines 49 to 53 of the referenced --743 patent "synthetic rubber compositions are ideal material for the subject tiles. Such compositions include the resilience and high coefficient of friction which enhance the textural, sound and other physical properties required for a tactile surface for the blind."
The second aspect is also mentioned in the above quote, relating to sound response of the tile. Prior art compositions of flexible polymers and rubber materials were specifically chosen because of the distinctive sound response made by walking on the rubber tiles. The contrast of sound produced from a pavement surface and the distinctive sound of the rubber tile was readily recognizable to the blind. This distinctive sound enabled the visually handicapped to recognize that they had just stepped onto a tactile tile, alerting this person to consider instructions provided by the tiles.
The use of flexible polymers and rubber compositions for tactile tiles has become an established practice in the industry. Initial use of rubber compositions arose with the early development of special design features for walking mats for stairs. For example, U.S. Pat. No. 348,782 issued in 1886 and 873,420 issued in 1907 disclosed the value of such compositions for stair treads. This material was applied in the highway environment for directing traffic as taught in U.S. Pat. No. 2,018,260 issued in 1931. Other efforts to shift away from the rubber compositions for walking surfaces have not met with any level of success. For example, U.S. Pat. No. 2,421,171 teaches the use of a thin steel plate with raised bumps for a stair tread, but has not received commercial acceptance.
With the emergence of tactile tile as a tool for assisting visually handicapped persons, the same tradition of rubber compositions was carried forward. U.S. Pat. No. 4,080,087 issued in 1978 disclosed a foot tile that was designed to give direction to a blind person. These tiles were recommended to be of polymers used in the highway industry prior to 1977, which were of flexible, resilient type materials. In the early 1980's the Japanese introduced tactile tiles in Japan and adopted the standard rubber-like composition which has become characteristic in the industry. In 1985, this same synthetic rubber became the specified composition in the federal specification for Tactile Mobility Aids for the Blind, specification number TT101. The use of synthetic rubber and similar flexible polymers has been the standard for tactile tiles up to the present time.
This is not to say that other polymers have not been present within the public safety arena. In 1978, the named inventor herein introduced the first fiberglass delineator for traffic control under U.S. Pat. No. 4,092,081. This was a direct contrast with pre-1978 polymers because this fiber reinforced, thermosetting polymer composite was rigid as opposed to flexible. In fact, short lengths of less than one foot, were almost as stiff as steel. Although it was considered suitable as a guide strip for traversing an intersection (U.S. Pat. No. 4,715,743), there was no recognition of utility in the field of tactile tiles. Its function as a guide strip was to provide a straight track for contacting by a cane or cue of the visually handicapped pedestrian. It was not designed for foot traffic. The federal specification for this guide strip is identified as TT1004.
Where departures from the use of synthetic rubber or flexible polymers for textile tiles have been suggested, these have not included application of rigid composites of thermosetting plastics. For example, U.S. Pat. No. 4,620,816 issued in 1986 discloses the concept of tactile simulation over an entire walking surface. The recommended materials included carpet of differing heights or pebbles of differing size imbedded in concrete. It is clear that the feature of sound recognition was not a criteria in selection of tactile compositions under the teachings of this patent.
The commercial reality of the tactile tile market is evidenced by the preceding historical review. The same flexible, rubber-like materials which have dominated the stair tread/tactile tile market for over one hundred years remain the primary composition in use today. Even more interesting is the fact that despite hundreds of new compositions that have developed over the last decade, none have made a significant inroad as a replacement composition.
It should not be presumed that the reason for such faithful allegiance to flexible polymers is a total absence of dissatisfaction with the product. To the contrary, the use of flexible polymers continues to develop challenges with respect to tile placement and retention. The flexibility of such tiles frequently results in detachment around the periphery or at the corners. Flexible tiles also have a tendency to adversely respond to changes in temperature. In short, there continues to be problems with flexible tiles; however, a suitable alternative which provide correct sound and tactile response has not been identified.